As such a positioning apparatus, conventionally, there is a positioning apparatus described in Patent Literature 1 (WO2007/074737). This conventional art is structured as follows (see FIG. 19A and FIG. 19B of the Patent Literature 1).
A circular plug is projected upward from a main body of a housing. The circular plug is able to be inserted into a circular hole of a work pallet lowered from above. An insertion hole is opened, coaxially with the circular plug, in an upper portion of the housing, and a positioning rod is vertically movably inserted into the insertion hole. Further, a through hole is opened laterally in a peripheral wall of the circular plug, and a ball is radially movably supported in the through hole. A cam surface is formed on the positioning rod so as to face the ball. When the positioning rod is driven to be lowered, the cam surface pushes the ball radially outwardly, and thereby, the ball is pressed onto an inner periphery of the circular hole of the work pallet.